The problem with the idea that shooting cops is justified by police brutality is that the cops that have been wounded or killed likely have NO CONNECTION IN ANY WAY to the recent incidents in which police shot unarmed civilians.
Shooting these people isn't helping to ease any sort of tension. If anything, cops will now be more on-edge. This can't be defended any more than any of the recent unjustifiable use of deadly force that these goons are likely protesting. They're likely opportunists, but I can't be sure of that.